This invention relates to a flash-assisted photographing system, particularly to a flash-assisted photographing system which controls the amount of flash light to be emitted or flash firing amount in accordance with respective light amounts in a plurality of divided areas of a photographic view, and also a flash-assisted photographing system which enables a combination of a so-called flashmatic control of controlling the flash firing amount based on a distance to an object and a set aperture value and a light adjustment control of controlling the flash firing amount based on a measured light amount of the object to perform flash-assisted photography, and further a flash-assisted photographing system which enables a combination of a so-called flashmatic control of controlling the flash firing amount based on a distance to an object and a set aperture value and a multi-spot light adjustment control of controlling the flash firing amount in accordance with respective light amounts in a plurality of divided areas of a photographic view to perform flash-assisted photography, and moreover a device such as camera and flash for use in a flash-assisted photographing system.
There have been proposed multi-spot light adjustment control as an exposure control for flash-assisted photography. In the multi-spot light adjustment control, a photographic view is divided into a plurality of areas, and light amounts from respective areas are measured. The flash light amount is adjusted based on measured light amounts from the respective areas to assure proper exposure of a main object. The following publications disclose exemplary multi-spot light adjustment controls.
Japanese Unexamined Patent Publication Nos. 61-194430 and 61-215537 disclose a multi-spot light adjustment control in which a control brightness is calculated from a brightness at a center portion of a photographic view and a brightness at a peripheral portion of the photographic view, the brightness being measured at the time of locking the auto-exposure or detecting the focus condition, thereby adjusting the flash light amount in accordance with the calculated control brightness to properly exposure! a whole portion of the photographic view while the main object is positioned at the center of the view.
Japanese Unexamined Patent Publication No. 2-87127 discloses a multi-spot light adjustment control in which the amount of natural light is measured before firing the flash, and the light amount is adjusted for respective divided areas based on the natural light amount to assure a proper exposure of an object partially having a high bright portion.
Japanese Unexamined Patent Publication No. 3-233524 discloses a multi-spot light adjustment control in which focus condition is checked for respective divided areas, and weighting is uniformly applied to all the divided areas to provide uniform flash light over the photographic view to assure proper exposure of a main object when every area is detected not to be in the focus condition.
As mentioned above, the multi-spot light adjustment is carried out to assure proper exposure of a main object by dividing the photographic view into a plurality of areas, and adjusting flash light amounts with respect to respective divided areas. To perform accurate multi-spot light adjustment. however. it is necessary to detect the position of a main object in the photographic view and the distance to the main object precisely.
The multi-spot light adjustment control shown in Japanese Unexamined Patent Publication Nos. 61-194430 and 61-215537 determines a control brightness based on a brightness at a center portion and a brightness at a peripheral portion on the assumption that the main object is usually in a center of the photographic view. Accordingly, this control cannot provide proper light adjustment in the case that a main object is not in a center or in the case that an accurate measurement of distance to an object cannot be attained.
The multi-spot light adjustment control shown in Japanese Unexamined Patent Publication No. 2-87127 adjusts the light amount so as to reduce or eliminate the influence of excessive light, e.g., sun light in the daylight-synchronized photography. This control does not consider the position of a main object and the distance to the main object. Accordingly, this control cannot reliably provide proper light adjustment for a variety of photography conditions.
The multi-spot light adjustment control shown in Japanese Unexamined Patent Publication No. 3-233524 requires the detection of respective focus conditions with respect to divided areas. This makes the exposure operation more complicated. A reference area for the multi-spot light adjustment is placed on an area having a high focus accuracy. Accordingly, proper light adjustment is hard to be accomplished in the case that a main object is not in the high focus accuracy area.
In these conventional multi-spot light adjustment controls, further, a light adjustment level is determined in the auto-focus processing. Accordingly, the proper light adjustment cannot be assured for an object moved after the determination of light adjustment level.
As flash light emission control for cameras, moreover, there has been known the flashmatic control in addition to the light adjustment control.
In the flashmatic control (hereinafter, "FM control"), a guide number of a flash device is calculated based on a specified information such as an object distance and a set aperture value, and a light emission period is controlled based on the calculation result so as to control a flash firing amount. This control is influenced by the reflectance of the object and the background with less likelihood, but is largely influenced by a distance measurement precision and an aperture precision. Especially, in the case that a short focal length lens is used, the distance measurement result largely varies depending upon a fine error of a lens projection amount. As a result, the calculated guide number of the flash device has a low reliability.
On the other hand, in the light adjustment control, the flash firing amount is controlled in real time based on the flash light reflected by the object. This control is influenced by the distance measurement precision and the aperture precision with little likelihood, but is largely influenced by the reflectance of the object and the background.
Both flash firing controls have advantages and disadvantages. and it is difficult to perform an optimal flash light emission control for every photographic view and under every photographing condition. In order to solve such a problem, a flash-assisted photographing system adopting a combination of both flash firing controls has been proposed.
For example, Japanese Unexamined Patent Publication No. 58-223125 discloses a flash-assisted photographing system which adopts the FM control to control the flash firing when the focal length of the lens used is longer than a predetermined focal length (telephoto lens) while adopting the light adjustment control when the focal length of the lens used is shorter than the predetermined focal length (wide angle lens).
Also, Japanese Unexamined Patent Publication No. 58-224334 discloses another flash-assisted photographing system which has a first mode for controlling the flash firing by the FM control and a second mode for controlling the flash firing by the light adjustment control, and in which the first mode is automatically selected when a filter, intermediate adapter or like accessory having a characteristic of varying an amount of transmission light (transmission light amount varying characteristic) is mounted on the lens.
Further, Japanese Unexamined Patent Publication No. 3-149535 discloses a Flash-assisted photographing system which controls the flash firing by the FM control when the object distance is shorter than a predetermined distance, while controlling it by the light adjustment control when the object distance is longer than the predetermined distance.
These conventional controlling devices are basically designed to perform a suitable flash firing control by controlling the flash firing by switching the control between the FM control and the light adjustment control so as to compensate for a reduced precision of the FM control due to a light measurement error, a focusing error or the mounting of an accessory having a transmission light amount varying characteristic. Accordingly, when the compensation conditions are satisfied, this controlling device can perform a more precise flash firing control than the other controlling device adopting only one of the controls.
However, there are a variety of photographic views and photographing conditions of the flash-assisted photography, and cases where a suitable exposure control is performed by the FM control and cases where a suitable exposure control is performed by the light adjustment control are not necessarily clearly distinguishable. Thus, if it cannot be clearly determined which control should be preferably used, the prior art exposure control by the switching method may not be necessarily effective.
Also, in the case that the light adjustment control is selected and a main object stands in front of a high reflective wall and the high reflective wall is covered by light adjustment areas for the multi-spot light adjustment, light is exceedingly reflected from the high reflective background wall and an adjustment control value is set blow a proper value, resulting in an insufficient exposure for the main object. Under the multi-spot light adjustment control, conversely, in the case that a main object stands in front of a low reflective wall, and the low reflective wall is covered by multi-spot light adjustment areas, the light reflection of the background wall is too low and an adjustment control value is set above a proper value, resulting in an excessive exposure for the main object.
Accordingly, even in the switchable combination of the FM control and the light adjustment control using the multi-spot light adjustment, to assure proper flash exposure, it is preferable to take into consideration a relationship between light adjustment areas and a photographic view as well as the operation state of taking lens.
Further, in the switchable combination of the FM control and the light adjustment control, these two controls are independent of each other. Accordingly, each control cannot sufficiently compensate for the disadvantages of the other. For example, in the case that a control error occurs in the FM control, this control error directly influences the flash firing, with the result that a suitable exposure cannot be obtained. Similarly, in the case that the reflectance of the object is not suitable for the light adjustment control, a light adjustment level deviates from a suitable level, making it difficult to obtain a proper exposure.